However, respiration of yeast can also take place anaerobically. This process does not require oxygen and is referred to as fermentation. This process partially breaks down carbohydrates and it obtains a small amount of energy, again in the form of ATP. Pyruvic acid has to be broken down in respiration when formed by breaking down of glucose molecules, this can't be done in the same way as in aerobic respiration. When anaerobic respiration is taking place carbon dioxide and ethanol is formed. The reaction for this process is:
C6H12 O6 -> 2C2H5 OH + 2CO2 + ATP
Enzymes are biological catalysts; they are designed to help speed up the rate of many reactions without actually taking part in the reaction themselves, therefore being reusable. For enzymes to be useful in a reaction, the substrate needs to bind with the enzymes active site. The active site is specific for a certain type of substrate and there are many different types of enzymes, which are all specifically designed to fit a certain substrate. Enzymes are affected by certain different factors, such as concentration, temperature and pH.
When you increase the temperature the rate of reaction is said to increase. This is because the extra heat energy produced when raising the temperature is converted into kinetic energy, which means the molecules all move at an increased speed. The faster molecules mean that there are going to be more collisions in a certain amount of time, and also as the molecules have more energy so therefore when the enzymes collide with a substrate there is more chance of the collision being successful as there is more chance of the molecules having the right amount of energy needed to carry out the reaction. However at a certain temperature the enzymes can become denatured and no longer work. This is when the shape of the active site is permanently distorted which means that the molecule can no longer bind to the active site, therefore the reaction cannot take place.
In this experiment I will be testing the amount of carbon dioxide in the anaerobic respiration of yeast. The uncontrolled variable in this experiment is the temperature. The temperatures at which I will measure the carbon dioxide are: 20oC, 30oC, 40oC, 50oC, 60oC, and 70oC. This is because respiration is an enzyme controlled reaction and enzymes will denature at some of the higher temperatures, e.g. 60-70o. There are many variables (factors) that could affect my investigation such as:
- The amount of sugar in the yeast solution
- The volume of the yeast solution
- The volume of water in the water bath
- The type of sugar
The amount of sugar in the yeast solution will be controlled by using the same amount of sugar in each of the tests. The volume of yeast solution will be controlled the same way, making sure the same amount is used each time. The volume of water in the water bath will be controlled by making sure that I have measured the same amount of water each time. The type of sugar will be controlled simply by just using the same type of sugar each time (sucrose).
I predict that as the temperature at which the yeast is heated increases, the amount of carbon dioxide given off will also increase (until it reaches it’s optimum temperature). The optimum temperature will be about 40-45oC because it is closer than any other interval to our body temperature.
A catalyst will speed up the reaction taking place. A catalyst that drives a biological reaction is called an enzyme. The enzymes speed up the substrate molecule. However, enzymes are proteins, which means they will be denatured (damaged) by heat, so going past the optimum temperature wont help the reaction. Once the enzymes have been heated and denatured, this active site is destroyed. The ‘Lock and Key’ hypothesis details how the molecule that helps an enzyme to react and the enzyme fit together like a lock and key, but if the enzyme denatures they no longer fit together.
The ‘Kinetic’ theory states that particles move around more as the amount of energy they are given increases. This means that as the enzymes are warmed up (given energy), they move around more and collide with each other more frequently; therefore more reactions occur. In conclusion: as the temperature is increased there are more reactions.
- Pipettes and measuring cylinders
- Glass rod (This will be used to mix the solution during the experiment so all the glucose is broken down effectively)
- Delivery tube
- 250ml Beaker (Water bath)
- Bunsen burner
- Heat-proof mat
Apparatus set up
- Set up apparatus as shown in diagram
- Measure 20cm3 of the water/yeast solution into a test tube
- Heat water bath with first test tube in. Starting Temperature: 20oC
- When solution reaches 20oC, quickly put bung and delivery tube onto the test tube
- Time solution for 2 minutes.
- Record amount of carbon dioxide (cm3) in the blocked syringe
- Repeat stages 2, 3, 4, 5 & 6 at the different intervals up to 70oC
- Repeat entire experiment a further 2 times so that an average can be collected from the 3 sets of results.
To make sure I carry out my experiments fairly, I will ensure that I only manipulate the temperature factor. I will make sure:
- I keep the same equipment. Therefore the size, thickness and shape of the equipment will not affect either surface area or temperature.
- I will use the same batch of yeast, so I can ensure that it is the same freshness, the age and size of the yeast culture is the same and also that the concentration is the same.
- I will repeat each experiment three times, therefore I will have three different recordings which will ensure my results are accurate and any incorrect results are ignored.
- I will check my temperatures at all times to make sure that the experiments are carried out correctly. This will make my results more accurate.
- The volume of water I use in my beaker must also be the same as the time it takes to heat the water also affects the rate of respiration of the yeast. I need to check that the volumes are the same each time I do the experiment so it doesn't affect my results.
The results clearly show that the slowest respiration rate was at 20oC. This may be because the yeast activity is very slow and they do not have a great amount of kinetic energy. This would also suggest that the collisions taking place between the yeast and glucose molecules would also be lacking energy and in some cases a successful collision would not take place as there would not be enough energy to carry out a reaction.
As the temperature got higher it is clear that the respiration rate increased. This would be because the more heat energy would provide the particles more kinetic energy and they would move faster, having more collisions in a shorter amount of time. The collisions would also be more likely to be successful as there is more energy and it is likely that the higher amount of energy would be enough to trigger a reaction.
The very high temperatures 60oC and 70oC show that at these temperatures it is very unlikely that a reaction would take place. Although there is more energy and the particles would indeed be moving faster, the enzymes active site would be denatured at these temperatures, causing them to be unable to bind with the yeast and glucose particles, which means that the majority of the enzymes would be ineffective, thus causing the experiment to be extremely slow or stop completely.
From this graph I could deduce that the optimum temperature for yeast respiration was between 40oC and 50oC. by looking at my graph I can see that at 45oC there was about 6.8cm3 gas being produced, although my graph shows that 50oC is a more suitable temperature. I think that this could be an anomalous result.
I have thoroughly researched this experiment it has helped me find out what temperature is the most ideal for efficient yeast respiration. I have analysed my results and I conclude that the most efficient temperature for yeast to respire quickest is at 45oC. I conducted my experiment twice and these showed that the yeast worked best at 50oC, as shown in my results.
My background research showed that enzymes were very significant in yeast respiration, and also that yeast behaves very much like an enzyme. This in mind, I predicted that yeast would respire most effectively at approximately 40oC. My experiments suggested that 50oC was the optimum temperature for yeast respiration, which I feel is close to my initial prediction but not correct. Enzymes work best at 37oC, however there are many different types of enzymes which all have slightly different optimum temperatures. Yeast is also available in a wide variety, and logically would also have a range of optimum temperatures. Therefore it is not surprising that I have a slightly different optimum temperature than originally predicted, as it would have depended on the specific type of yeast I used.
In conclusion, I feel my prediction was accurate on the whole although my experiments havn’t quite correctly supported my background research and prediction. I feel that the experiments worked well. I feel that the investigation went well but wasn’t completely successful.
I feel that if I were to do the experiment again, I may want to repeat it for a further fourth time just to get a wider range of results. I would also want to carry out the entire experiment in one sitting, but during this experiment there wasn’t enough time. I may also chose to use methylene blue. This indicator is effective when judging if yeast is respiring, as it will go colourless when the oxygen content is reduced, which will be a clear indication that respiration is taking place. Overall, I am pleased with my experiment but feel that I could have obtained a more successful result.